Automatic infeed mechanism for centerless grinders



June 7, 1955 A. H. DALL ETAL 2,709,877

AUTOMATIC INFEED MECHANISM FOR CENTERLESS GRINDERS Filed Sept. '7, 1954 5 Sheets-Sheet 1 .INVENTORS.

ALBERT H, DALL Y GEORGE L, (move 0 I F Z ATTORNEYS.

A. H. DALL EI'AL 2,709,877

AUTOMATIC INFEED MECHANISM FOR CENTERLESS GRINDERS 5 Sheets-Sheet 2 m T E INVENTORS'. ALBERT H, DALL. BY GEORGE L. 6R0 VE ,v/Yf/m 2;

AT TORNEYS.

QQ A w u Q I A Q a 4%2/ 22%2;? w M i M g v g M2 53% RN mw Low 3 June 7, 1955 Filed Sept. 7, 1954 June 7, 1955 A. H. DALL ETAL 2,709,377

AUTOMATIC INFEED MECHANISM FOR CENTERLESS GRINDERS Filed Sept. 7, 1954 5 Shees-Sheet s A T TORNE Y8.

June 7, 1955 A. H. DALL ETAL 2,709,877

AUTOMATIC INF'EED MECHANISM FOR CENTERLBSS GRINDERS Filed Sept. 7, 1954 5 Sheets-Sheet 4 l E i g. 5'

' INVENTORS.

ALBERT H, DALL GEORGE L, GROVE ATTORNEYS.

United States Patent AUTOMATIC INFEED MECHANISM FOR CENTERLESS GRINDERS Albert H. Dali and George L. Grove, Cincinnati, Ohio,

assignors to The Cincinnati Milling Machine Co., Cinciunati, Ohio, a corporation of Ohio Application September 7, 1954, Serial No. 454,312 11 Claims. (Cl. 51-165) This invention relates to grinding machines and more particularly to improvements in automatic infeed mechanisms for centerless grinding machines and the like.

One of the objects of this invention is to provide an improved and simplified automatic infeed mechanism for a centerless grinder.

Another object of this invention is to provide a new and improved fluid pressure operated infeed mechanism having a closed circuit to minimize the flow of oil and keep down the temperature of the machine.

A further object of this invention is to devise a new and improved pneumatic-hydraulic automatic infeed mechanism for a centerless grinder.

Other objects and advantages of the present invention should be readily apparent by reference to the following specification, considered in conjunction with the accompanying drawings forming a part thereof, and it is to be understood that any modifications may be made in the exact structural details there shown and described, within the scope of the appended claims, without departing from or exceeding the spirit of the invention.

Referring to the drawings in which like reference numerals indicate like or similar parts:

Figure 1 is an elevational view of a centerless grinding machine embodying the principles of this invention.

Figure 2 is a vertical section on the line 2--2 of Figure 1.

Figure 3 is a vertical section through the feed screw as viewed on the line 3-3 of Figure 2.

Figure 4 is a detail section as viewed on the line 4-4 of Figure 3.

Figure 5 is a detail of Figure 3.

Figure 6 is a diagrammatic view of the pneumatichydraulic infeed circuit.

Figure 7 is a view showing the dog arrangement for effecting a tarry during rapid traverse advance.

Figure 8 is a view showing the dog arrangement for effecting a dwell in the feeding part of the cycle.

Figure 9 is a view showing the dog arrangement for effecting a shortened stroke.

Figure 10 is a diagrammatic view of the electric control circuit.

In Figure 1 of the drawings the reference numeral 10 indicates the bed of a centerless grinding machine embodying the principles of this invention upon the top of which is mounted a grinding wheel 11, a workrest blade 12 and aregulating wheel 13. The grinding wheel is enclosed in a suitable housing 14 and rotated by conventional power driving mechanism not-shown. The regulating wheel 13 is enclosed in a bracket 15 which is adjustably mounted on the front of a slide housing 16. The housing 16 carries conventionalpower driving mechanism, not shown, for rotating the regulating wheel.

In a centerless grinding machine a workpiece, such as 17, is supported on the workrest 12 between the grinding wheel and regulating wheelyand to effect grinding, the workrest blade 12 and the regulating wheel 13 are in section as viewed on the line 5--5 2,709,877 Patented June 7, 1955 some cases jointly moved toward the grinding wheel 11, while in other cases, only the regulating wheel is moved. This depends mostly on the size of the work. For adjustment purposes, the slide 16, as shown in Figure 2, is provided with guide surfaces 17 which engage a dovetailed guide 18 formed on the top of a lower slide 19. The lower slide, in turn, has dovetailed guide surfaces 20 which move on a dovetailed guideway 21 formed on the bed 10 of the machine. As shown in Figure 1, the workrest blade 12 is mounted on the lower slide 19, and since, as shown in Figure 3, all movement is imparted to the upper slide 16 by the feed screw 22, for joint movement of both, the lower slide is clamped to the upper slide by the clamping means 23 as shown in Figure 2. On the other hand, when it is desired to adjust only the regulating wheel 13 with respect to the workrest blade 12, the upper slide 16 is unclamped from the lower slide, and the lower slide is clamped to the bed by a second clamping means 24.

When grinding work by the infeed method, as distinguished from the through feed method in centerless grinders, the work remains stationary axially and the face of the regulating wheel is substantially parallel to the face of the grinding wheel.

By means of this invention, the regulating wheel and workrest are moved through an automatic infeed cycle to and from the grinding wheel, first at a rapid traverse rate to move the Work into engagement with the grinding wheel; then at a feeding rate to eifect the grinding operation; and after a predetermined dwell, if so desired, a rapid return motion is effected to return the parts to a starting or loading position. In this machine the upper slide 16, which carries the regulating wheel, has a main feed screw 22 threaded in a rotatable nut 25, as shown in Figure 3, which nut is in the form of a sleeve provided with anti-friction thrust bearings 26 and 27 and journaled in the bearing 28 formed in the housing 16. The nut sleeve has a tubular extension 29 to the end of which is secured a bevel gear 30 by suitable screws 31. This gear meshes with a bevel gear 32, shown in Figure 2, which is mounted on the end of a shaft 33 journaled in the slide 16 and operable by a hand wheel 34 shown in Figure 1. The screw 22 is anchored against axial movement in a bracket 35 attached to the end of the bed 10, as shown in Figure 3, by suitable bolts 36. As shown, the screw 22 has a reduced portion 37 upon which is mounted a thrust bearing 38 engaging the shoulder 39 of the bracket, while the other side of the thrust bearing engages the shoulder 40 on the screw.

The screw has a secondreduced portion 41 which passes through a bore 42 formed in the bracket, and on the other side of the bore a gear 43 is secured to the screw by a suitable key 44 and nut 45 which may be adjusted to hold the screw against axial movement, the face 46 of the gear bearing against the face 47 of the bracket. It will now be apparent that with the screw 22 held against axial movement, rotation of the handwheel 34 through the gearing 32, 30 will cause rotation of the nut in one direction or the other to cause movement of the slide 16, and of the lower slide 19 if clamped thereto as previously explained.

To eliminate backlash between the screw 22 and its nut, a second nut member 48, Figure 3, is threaded on the screw, and a spring 49 is mounted between the nut member 48 and a-threaded member 50 which is internally threaded at 51 in the gear 30. By rotation of the member 50, the compression of spring 49 may 'be adjusted to take out backlash between the nut 25 and the screw 22. The member 48 is confined for rotation with the nut 25 by a set screw 52 threaded in the sleeve portion 29 and engaging any one of av series of longitudinal slots 53 cut in the periphery of the member 48.

A locking member 54 surrounds the sleeve portion 29 and is held against axial movement by rings 55 and 56. The clamping member 54 is split, as shown in Figure 2, and a set screw 57 is threaded in the housing 16 for engagement with a fiat 58 formed on the member 54 to prevent rotational movement thereof in one direction. Opposite the set screw 57 is a locking screw 59 which is threaded in the housing 16 and provided with an operating handle 60 for rotation into engagement with a second flat 61 formed on the member 54 whereby the latter may be squeezed to securely hold the nut 25 against rotation.

From the foregoing it will be seen that if the nut mc1nber 25 is locked against rotation by the clamping screw 59, rotation of the screw 22 by the gear 43 will cause movement of the slide 16 or, on the other hand, if the locking screw 59 is released and the screw 22. held against rotation, that the hand wheel 34 may be utilized to rotate the nut relative to the screw 22 and thereby cause feeding movement of the slide 16.

The automatic power operated infeed cycle is effected by clamping the screw 59 and power rotating the screw 22 through the medium of the gear 43. To this end the gear 43, as shown in Figure 5, intermeshes on opposite sides with rack pistons 62 and 63. The piston 62 is reciprocable in the cylinder 64, and the piston 63 is reciprocable in the cylinder 65, both cylinders being formed in the bracket 35, and it will be obvious that it is only necessary to admit pressure to one end of these cylinders due to the gear interconnection to effect move ment in either direction. Thus, if pressure is admitted to the port 66 of cylinder 64, the piston 62 will move upward as viewed in Figure 5 and through the gear connection cause downward movement of the piston 63. Similarly, if pressure is admitted to port 67, the piston 63 will move upward, and through the gear connection the piston 62 will move downward. Actuation of the pistons is effected by closed hydraulic circuits in which a cylinder 68 is provided as shown in Figure 6, which has a first chamber 69 connected by channel 70 to port 66 of cylinder 64, and a second chamber 71 which is con-- nected, by a channel 72 and suitable control valves, to port 67 of cylinder 65.

The cylinder 68 contains a tandem piston comprising piston head 73 and piston head 74 connected together by a piston rod 75. The piston rod is slidably mounted in a fixed block 76 held in position in the cylinder by snap rings 77 and 78 and serving to separate the chamber 71 from the chamber 69. The cylinder has end chambers 79 and '80. The method of operation consists i of admitting compressed air to either chamber 79 or 80 to cause movement of the tandem piston, and this effects transfer of oil contained in one of the chambers 71-69 to its respective piston whereby movement of one of the pistons 62, 63 will cause, through the rack and gear connection between them, a transfer of oil back to the other chamber in the cylinder 68. The channels 70 and 72 are merely kept supercharged with oil enough to compensate for leakage by a pump 81 having an intake 82 for withdrawing oil from a reservoir 83 and delivering it under pressure to two check valves 84 and 85 connected respectively to channels 72 and 70 respectively. A relief valve 86 is connected to the output of pump 81 for maintaining a predetermined constant pressure at the relief valves.

When the tandem piston moves upward, as viewed in Figure 6, the oil in chamber 71 is forced through channel 72 to port 87 of a feed-rapid traverse selector valve 88, and when the valve plunger 89 is in the position shown, the port 87 is connected to port 90. The oil thus flows directly to channel 91 and port 67 of cylinder 65. This will cause upward movement of the piston 63 at a rapid traverse rate and through the gear 43 downward movement of piston 62 in cylinder 64. This will force the oil in chamber 64 through port 66 and channel 70 to chamber 69, the volumetric capacity of which is increasing, thereby reducing the back pressure in channel 70.

At a predetermined time in the cycle, the valve plunger 89 is moved downward, thereby isolating port 90, and connecting port 87 to port 92. The fluid pressure now flows through channel 93 to the rate control valve 94 which may be of any well-known construction, that found in Letters Patent 2,622,614 being suitable for present purposes. The fluid pressure then continues through channel 95, check valve 96, to channel 91. The piston 63 will then move at a feed rate, and the oil will still return through channel 70 to chamber 69.

Attention is invited to the fact that the piston rod 75 has an axial bore 97 which is closed at opposite ends by check valves 98 and 99. The piston rod 75 also has a pair of radial ports 100 and 101 which intersect the bore 97 on opposite sides of the check valve 98, and a second pair of radial ports 102 and 103 which intersect the bore 97 011 opposite sides of the check valve 99. Normally the ports 101, 102 are not uncovered, but if the tandem piston gets too far out of step with the rack pistons, oil will be transferred from one side of the circuit to the other to assist in centralizing the tandem piston.

The air valves, indicated generally by the reference numerals 104 and 105, are automatically operated by their respective solenoids 106 and 107. A source of air pressure, which may be indicated generally by the valve 108, is connected by channels 109 and 110 to ports 111 and 112 of the respective air valves. The valve 104 has a valve plunger 113 which is normally held by a spring 114 to connect pressure channel 109 to port 119 and channel 115 leading to port 116 of cylinder 68. The other valve 105 has a valve plunger 117 which is normally held closed by a spring 118. At the end of the feeding stroke the solenoids 106 and 107 are simultaneously energized to close the port 111 and connect the port 119 to exhaust port 120. When the valve plunger 117 is actuated, it disconnects port 121, which is connected by channel 122 to port 123 leading to chamber 79, from the valve exhaust port 124; and connects the pres sure port 112 to port 121.

When the air pressure enters chamber 80 the tandem piston will move down, forcing the fluid in chamber 69 into piston chamber 64 and thereby through the rack and gear connection, cause the piston 63 to force the oil therein back to chamber 71 of cylinder 68 but through the check valve 125 to line 72, thereby bypassing the feedrapid traverse selection valve.

For the further understanding of the complete operation of this invention, attention is directed to the fact that the line 72 has a selector valve 126 serially connected therein, and when the valve plunger 127 is in the position shown in Figure 6, the line 72 is directly connected to port 87. Upon rotation of the valve plunger by its lever 128 to the position indicated by the dotted line 129, line 72 is connected by the valve groove 130 to line 131, and line 72A is connected by the valve groove 132 to channel 133. The channels 131 and 133 terminate in a stop valve 134 which has a valve plunger 135 that is normally held open by a spring 136, and adapted to be closed by a solenoid 137. When the stop valve 134 is serially connected in the line by valve 126 and the plunger 135 is raised to stop the flow from channel 131 to channel 133, a back pressure is created in cylinder 71 which is suflicient to overcome the air pressure in cylinder 79 and stop the movement of the tandem piston which, in turn, will stop the movement of the rack pistons 63 and 62.

There arevarious cycles of operation that can be effected by this mechanism dependent upon the setting of dogs on the dog wheel 138 which, as shown in Figure 3, is integral with the gear 43. This wheel has a dovetailed groove 139 in which arefitted dogs 140 and 141. The simplest cycle of operation is asingle cycle comprising a rapid traverse movement, a feed movement, dwell, and rapid traverse return. This will be explained in connection with the electrical circuit shown in Figure 10. For this cycle of operation only one dog, 140, is mounted on the dog wheel 138 as shown in Figure 4. In Figure 6, the parts are shown in the return stop position, and it will be noted from that figure that air pressure is connected to the cylinder 80 tending to force the piston 73 downward thereby forcing the fluid in chamber 69 into cylinder 64 and since the piston 62 is at the end of its stroke and can go no farther, the piston 73 is stopped in its movement because the pressure in cylinder 69 has risen to the point where it is greater than the air pressure in cylinder 80. It will thus be seen that the parts are held in this position until the next cycle is started. The regulating wheel is, of course, held in a retracted position with respect to the grinding wheel preparatory to the next cycle of operation.

For a single cycle of operation, the valve plunger 127 in Figure 6 will be in the position shown, and in the electrical diagram in Figure the circuit is set up for a single cycle of operation by closing a switch 142 in a line 143. A start button 146, when closed, connects the main line 145 through stop switch 144, line 147, and normally closed timer switch TR1-1 of timer relay TR1, to control relay CR1 which in turn is connected to the other main line 143. The energization of control relay CR1 closes its latching contact CR1-1 around start button 146 and thereby latches the circuit for release of the start button 146.

The control relay CR1 also closes its contact CR1-2 in line 149, causing energization of solenoids 106 and 107. These solenoids are connected to the air valves shown in Figure 6, thereby reversing the pressure in chambers 79 and St to cause movement of the tandem piston at a rapid traverse rate. This will produce rotation of the dog wheel 138 until the dog 140 hits the plunger 150 shown in Figure 4 to depress the valve plunger 89. This will move the valve plunger 89 downward until the spool 151 passes the pressure port 87 whereby fluid pressure will be admitted to the groove 152 and flow through the port 92 to the rate control valve 94. At the same time the fluid pressure will flow through the cross bore 153 and axial bore 154 in the plunger 89 to the chamber 155 which will thereby separate the plunger 150 from the valve plunger 89. In other words, the valve is self-actuated in the sense that the plunger 89 will now move downward to its extreme position defined by the shoulder 155 and against the compression of spring 156. At the same time the plunger 150 will automatically be moved upward as soon as the dog 140 has passed out of engagement therewith. The cycle will now continue at a feed rate.

The end of the feeding movement is reached when the piston 63 reaches the end of cylinder 65, as shown in Figure 5, at which time it will operate the limit switch LS-l. The closing of this switch, as shown in Figure 10, will complete a circuit through line 143, switch 142 to the timer relay TR1. Operation of this relay will open the normally closed contact TR1-1 in line 147, thereby breaking the circuit to control relay CR1. This relay will then open its contact CR1-2 in line 149, deenergizing solenoids 106 and 107 of the air valves whereby they will resume their position shown in Figure 6, and the tandem piston will execute a return stroke to the starting position.

It is obvious in this cycle that, if switch 142 is left open when the piston 63 completes its stroke and the regulating wheel is advanced to its extreme position, that the parts are set up for throughfeed grinding, and LS1 Will become inefiective to cause a return movement until the switch 142 is closed.

To set up the cycle for continuously repeating operations, both of the electrical switches 142 and 157 in Figure 10 are closed whereby upon operation of timer relay TRI at the end of the infeeding movement the contact TR1-2 is closed, causing energization of relay CR2. This relay will immediately close its contact till CR2-2, completing a latching circuit around TR1-2. The relay CR2 will also close its contact CR2-1 in branch line 158. At this time contact TR1-1 has opened and closed to break the circuit to relay CR1 and open its latching contact CR1-1 which is connected in parallel with contact CR2-1. The cycle continues to eifect retraction of the regulating wheel until the rack plunger 62 reaches the end of its stroke and operates limit switch LS2. As shown in Figure 10, the limit switch is in line 159 for operation of timer relay TR2. This line, however, has a selector switch 160 which is coupled with a selector switch 161 in line 162 and are simultaneously operated by a control lever 163. When the switch 160 is closed, the closing of limit switch LS2 will energize the timer relay TR2. This relay has a timed closing to provide the neces- V sary delay before the starting of the next cycle to permit the operator to load the machine. When the relay finally actuates, it closes contact TR2-1, which is serially connected to contact CR2-1 in line 158, which is already closed, thereby completing a circuit through line 147 to control relay CR1 which automatically starts the next cycle.

Provision has also been made for stopping the infeed movement either during the rapid traverse portion of the cycle or the feeding movement of the cycle. In Figure 7, the dogs and 141 are shown positioned on the dog wheel 138 to eifect a stop during the rapid traverse movement. In this figure the dotted position 164 of dog 140 indicates the starting position and when the dog wheel has rotated through a desired angle, such as 165, which is selectable at will, the dog 141 will be positioned to operate the limit switch LS3. The limit switch LS3 is connected as shown in the electrical circuit, Figure 10, for operation of the solenoid 137 which, as previously described, causes closing of the stop valve 134.

At this time, of course, the selector switch 161 is closed so that upon closing of LS3 the solenoid 137 is immediately actuated, and a timer relay TR3, connected in parallel with solenoid 137, is also energized. This relay has a contact TR3-1 in the line 166 which is normally closed. The relay TR3 is timed to operate after a predetermined dwell selectable by the operator and then it opens contact TR3-1 whereby the solenoid 137 is deenergized, and the stop valve opens so that the rapid traverse movement may continue. The dog 141 will immediately pass out of engagement with the limit switch LS3 thereby deenergizing relay TR3 so that the contact TR3-1 will immediately close preparatory to the next cycle.

When it is desired to effect a dwell in the feeding part of the cycle the dogs 140 and 141 are attached to the dog wheel 138 in the manner shown in Figure 8 whereby the dog 141 will operate the limit switch LS3 during the feeding part of the cycle producing the same stopping effect.

It has been found desirable when particularly fast cycles of operation are desired to shorten the length of the return movement, and in this case the dog 141 is removed from the dog wheel and another dog 167, as shown in Figure 9, is attached to the dog wheel. In this figure the dogs 140 and 167 are shown in the starting position and due to the shortened length of the infeed movement it will be noted that the dog 140 has not returned to its normal starting position indicated by the line 168. In other words, upon clockwise rotation of the dog wheel 138 during the return movement the dog 167 will approach the limit switch LS3 but at this time the selector switch 161 is moved to its dotted line position connecting the line 162 to line 168 whereby the limit switch LS3 is now operatively connected for actuation of timer relay TR2. Therefore, this timer relay will be energized earlier in the return movement than if it was operated by limit switch LS2.

It will now be evident that if the timer relay TRZ closes its contact TR2-1 that the return movement will be immediately reversed and the next infeeding cycle started before the regulating wheel slide has reached its normal return position.

The choice of cycle tobe used is dependent upon certain factors such as the size of the work to be ground, the method of unloading the work and whether one or both slides are to be moved during the cycle.

In a centerless grinder, when the work is loaded it must be supported by the workrest blade and the regulating wheel, and, dependent upon the size of work, it is obvious that they must be close enough together that the workpiece does not fall down between the blade and wheel. When both slides are used, they are clamped together and moved as a unit to move the workpiece into engagement with the grinding wheel. In this method there is no variation between the spacing of the blade and the regulating wheel. Therefore, the workpiece must be moved endwise after retraction from the grinding wheel in order to unload the workpiece.

When only one slide is utilized, the lower slide which supports the blade is adjusted during set-up of the machine to place the blade in its final position with respect to the grinding wheel, which is the same position it would assume at the end of the advance stroke when both slides operate jointly. Thus, the regulating wheel moves back and forth, not only with respect to the grinding wheel, but also with respect to the workrest blade. It is obvious that after a workpiece has been ground to size and the regulating wheel is retracted that the workpiece will roll down the slope of the workrest blade as the space between the regulating wheel and the blade widens. If the workpiece is small and the maximum retraction between the regulating wheel and the blade is greater than the diameter of the work, the workpiece will fall between the blade and the regulating wheel and thus be automatically unloaded from the machine. Under this condition, it will be impossible, however, to load the next workpiece until the regulating wheel has been advanced sufficiently to close the gap between the blade and the wheel sufficient to support it. Thus, in one cycle arrangement, provision has been made for a stop during the rapid traverse approach movement so that the workpiece may be loaded. Obviously, as the regulating wheel continues its approach it rolls the work higher on the workrest blade.

It will thus be seen that a simple and compact infeed mechanism has been devised for rotating a feed screw which is initially actuated by air pressure acting on a hydraulic mechanism, in which the rate of movement is controlled in the hydraulic mechanism rather than in the pneumatic mechanism, and thus the effects of adiabatic expansion of the air are eliminated. Although the mechanism is fundamentally a constant stroke mechanism, suitable controls have been provided for effecting a reverse during retractive movement prior to completion of the entire retractive movement which, in efiect, shortens the stroke of the mechanism, thus producing a saving in time for the total cycle whenever conditions make it possible to do so.

What is claimed is:

l. in a centerless grinding machine having a grinding wheel mounted on a bed, a workrest blade, and a regulating wheel, the combination with a slide supporting the regulating wheel for cyclic movement toward and from the grinding wheel, of a feed screw journaled in the bed against axial movement and having a threaded connection with said slide, an operating gear fixed on the screw, rack plungers operatively engaging opposite sides of the gear, means to apply fluid pressure to one of said plungers to eflect rotation of the gear and advance the slide, and means to apply fluid pressure to the other plunger to retract the slide.

2. In a centerless grinding machine having a bed, a grinding wheel rotatably mounted on the bed, a workrest slide mounted on the bed and having a workrest blade, a regulating wheel, a slide for the regulating wheel mounted on the workrest slide, the combination of a feed screw journaled in the bed against axial movement and having a threaded connection with said regulating wheel slide, means to connect the regulating wheel slide to the other slide for joint movement, an operating gear fixed on the screw, rack plungers operatively engaging opposite sides of the gear, means to apply fluid pressure to one of said plungers to effect rotation of the gear in one direction to advance the slide, and means to apply fluid pressure to the other plunger to retract the slide.

3. In a centerless grinding machine having a regulating wheel movable to and from a grinding wheel for infeed grinding operations, the combination of a feed screw operatively connected for movement of the regulating wheel, means to effect rotation of the screw including a gear keyed thereto, a pair of rack plungers operatively engaging opposite sides of the gear, fluid pressure cylinders containing said plungers, a master cylinder having collapsible chambers connected respec' tively to said cylinders in closed circuits, and means to collapse one chamber and expand the other to effect opposite movement of said plungers and rotation of said screw.

4. In a centerless grinding machine having a regulating wheel slidably mounted on a bed for movement toward and from a grinding wheel to effect infeed grinding cycles, the combination with a feed screw journaled in the bed and operatively connected for movement of the regulating wheel, of a gear keyed to said screw, means including fluid operated plungers and cylinders mounted in the bed and operatively connected to opposite sides of said gear for effecting opposite directions of rotation thereof, a master cylinder having tandem pistons slidable therein, an intermediate head fixed between said pistons to create independent chambers, means connecting said cylinders to the respective chambers in closed fluid circuits whereby movement of said pistons will force fluid pressure to one of said plungers and withdraw fiuid pressure from the other plunger.

5. An infeed cycle control mechanism for a centerless grinder having a regulating wheel movable toward and from a grinding wheel comprising a feed screw for cf fecting said movement, an operating gear attached to said feed screw, a pair of rack plungers meshing with said gear, cylinders containing said plungers, a master cylinder having tandem pistons s'lidable therein, an intermediate' cylinder head between said pistons creating independent chambers, means connecting the chambers to the respective cylinders in a closed circuit arrangement, each closed circuit being filled with operating fluid whereby reciprocation of said pistons will force fluid to one plunger and withdraw fluid from the other, said master cylinder having end cylinder heads creating operating chambers to effect reciprocation of said tandem pistons, and means to reversibly connect said operating chambers to a source of operating pressure.

6. An infeed cycle control mechanism for a centerless grinder for moving a regulating wheel toward and from a grinding wheel, comprising a feed screw operatively connected to effect said movement upon rotation thereof, a gear connected to said screw, fluid rack plungers meshing with said gear, means to supply fluid pressure to one of said plungers to effect rotation of the screw in a direction to advance the regulating wheel, said means including a feed rate control valve, a selector valve for operatively connecting the rate valve in or out of the circuit to change the rate of movement, a dog wheel integrally formed with said gear, and means carried by the dog wheel for shifting said selector valve.

7. In an automatic infeed mechanism for a grinding machine having 'an infeed operating screw, the combination with a gear attached to said screw, of a pair of rack pistons meshing with opposite sides of said gear, hydraulic control means for delivering fluid pressure to one of said pistons to effect rotation of said screw, electrically operable valve means to reverse said control means to deliver fluid pressure to the other of said pistons, and switch means operable by the first-named piston to cause operation of said electrically operable means.

8. In an automatic infeed mechanism for a grinding machine having an infeed operating screw, the combination with a gear attached to said screw, of a pair of rack pistons operatively connected to opposite sides of said gear to effect opposite rotation of said screw, hydraulic control means including a channel for delivering fluid to one of said pistons at a rate to effect rapid traverse operation of said screw, a rate valve, selector valve means operable to connect said rate valve serially in said channel to effect a feed rate, a dog wheel rotatable by said gear, and means on said wheel to effect actuation of said selector valve means.

9. In an automatic infeed mechanism for a grinding machine having an infeed operating screw, the combination with a gear operatively connected to said screw, of hydraulically operable means to efiect rotation of said gear, electrically operable control valve means therefor having a normal position causing retractive rotation of said gear, a first manually operable switch having circuit connections to said electrically operable valve means to reverse the position of said valve means to cause infeed rotation of said gear, an automatically operable second switch in said circuit connections to break said circuit to cause retractive rotation of gear, and a third switch automatically operable to reestablish said circuit connections to cause infeed rotation of said gear before the retractive rotation has been completed.

10. In an automatic infeed mechanism for a grinding machine having an infeed operating screw, the combination with a gear operatively connected to said screw, of hydraulically operable means to effect rotation of said gear, electrically operable control valve means therefor having a normal position causing retractive rotation of said gear, a first manually operable switch having circuit connections to said electrically operable valve means to reverse the position of said valve means to cause infeed rotation of said gear, an automatically operable second switch in said circuit connections to break said circuit to cause retractive rotation of gear, a third switch automatically operable to reestablish said circuit connections to cause infeed rotation of said gear before the retractive rotation has been completed, and a dog wheel rotatable by said gear having means for operating said second and third switch.

11. In an automatic infeed mechanism for a grinding machine having an infeed operating screw, the combination with a rack piston operatively connected to said gear to effect infeed rotation thereof, channel means connected to said piston for delivering fluid pressure thereto at a rate to effect a rapid traverse movement, a feed rate valve, selector valve means to connect said feed rate valve serially in said channel means, a stop valve, means to serially connect said stop valve in said channel means. electrically operable means for closing said stop valve to institute a delay in said movement, and automatically operable means responsive to rotation of said gear to eflect sequential operation of said selector valve and said electrically operable means.

References Cited in the file of this patent UNITED STATES PATENTS 1,976,111 Binns et a1. Oct. 9, 1934 2,004,426 Booth et al June 11, 1935 2,049,611 Harrison et a1. Aug. 4, 1936 

